One- and two-color three-pulse photon echo studies of protein and liquid dynamics

The three Pulse Photon Echo Peak Shift (3PEPS) spectroscopic technique has been used to study the dynamics of energy transfer in the various light harvesting complexes (LHCs) of plants and photosynthetic bacteria. The mechanism and timescales of energy transfer in the LHCs depend on the electronic coupling between the pigments, the coupling of the pigments to the bath fluctuations and the distribution of pigment static site energies. The 3PEPS technique has been shown to be remarkably sensitive to these factors and by combining experiments with theory information about the dynamics in the LHCs at the microscopic level is retrieved.; 3PEPS data on the light-harvesting complex (LHCII) from a green algae Chlamydomonas reinhardtii revealed energy transfer between the Chls a and between one pair of Chls b. Wavelength dependent 3PEPS data for the B800 band of LH2 complex of the purple bacteria, Rps. acidophila displayed energy transfer within the B800 band (∼500 fs) that can be quantitatively explained by the Förster theory. A novel technique was developed to account for the multichromophoric, weakly coupled energy transfer system via the coupled master equation and third order optical response function approach. It was also shown that the disorder in the ensemble of rings is distributed in two ways; the distribution of static site energies within the aggregate and another distribution of the mean energy of the rings in the ensemble.; Temperature dependent 3PEPS data for a strongly coupled B820 ring of the species Rps. acidophila, strain 7750 shows that the exciton relaxation rate is independent of temperature. The disordered exciton theory does not explain the temperature independence of the relaxation rate and it is suggested that exciton relaxation may occur by a multi-phonon process.; Comparing the 3PEPS data between the LH2 complexes that were detergent isolated and in native membranes showed that energy transfer between the LH2 complexes in membranes takes place on a timescale of 5 ps. The LH2 complexes in membranes exhibit a pronounced second level of disorder (due to a distribution of mean energies of individual LH2 rings). This behavior is argued to be due to different environments and a range of inter-complex interactions experienced by the LH2 complexes in membranes.; A Two-Color 3PEPS (2C3PEPS) experimental technique has been developed. The 2C3PEPS technique can be used to probe correlation in electronic transitions in two different regions of the electronic spectrum of a chromophore in the condensed phase. In dyes dissolved in liquids, no correlation between the two spectral regions was observed at short times, and a gain in correlation is observed owing to ultrafast solvent motion. The memory of the transition frequency is partially conserved during the spectral diffusion process. The technique can be used to probe the transfer of nuclear memory between reactants and products during a chemical reaction.